diff --git a/Doc/library/webbrowser.rst b/Doc/library/webbrowser.rst
index 4250598aa2d..af8b637d5b7 100644
--- a/Doc/library/webbrowser.rst
+++ b/Doc/library/webbrowser.rst
@@ -55,6 +55,10 @@ The following functions are defined:
    under many window managers this will occur regardless of the setting of this
    variable).
 
+   Note that on some platforms, trying to open a filename using this function,
+   may work and start the operating system's associated program.  However, this
+   is neither supported nor portable.
+
    .. versionchanged:: 2.5
       *new* can now be 2.